Many polymeric interlayer materials and lamination designs have been described for use in automotive and architectural glazing applications. Industry, government and customer specifications for safety, impact resistance, ultraviolet and infrared light blockage, moisture resistance, haze or optical clarity, sound transmission, weight and thermal transmission direct the selection of materials and designs for particular glazing products. In general, manufacturers require lighter weight, thinner glazing products for automotive assembly than for architectural uses.
Impact resistance and controlled patterns of glass shattering are specified safety parameters for automotive glazing products. To meet these parameters, automotive glazing products are generally constructed of a multi-layer laminate of a glass sandwich containing a polymeric interlayer film. Many automobile-makers require security or anti-theft properties in glazing products in addition to mandatory safety properties. For deterring unauthorized entry into a vehicle, to lessen the likelihood of a person being thrown from a vehicle during an accident and for acceptable security functionality, the glazing products must possess high penetration resistance and high rigidity after glass breakage.
Among the polymeric interlayer materials described as useful in security and safety glass laminations are the high modulus xe2x80x9cionomeric resinxe2x80x9d materials used as a film interlayer between two rigid transparent sheets in the manner described in U.S. Pat. No. 4,668,574. In general, an adhesion promoter, e.g., a silane primer, is needed to laminate the ionomeric resin to glass, and the ionomeric resin is preferably cross-linked, e.g., with a diamine, to increase its effective use temperature, to improve glazing clarity and to reduce haze, as described in U.S. Pat. Nos. 4,619,973 and 4,663,228. The mechanical barrier properties of the ionomeric resin laminates are superb. They are used in bullet-proof glazing and other very demanding security applications. As described in U.S. Pat. No. 5,763,062, the superior transparency of the ionomeric resins, particularly newer resins having a higher acid content (e.g., at least 17 wt %), or those resins modified with diamine cross-linking, permits use at a relatively large film thickness, on the order of 1-4 mm, in optically transparent laminates.
While useful as security barriers, the ionomeric resin films and laminates made with such films are poor acoustical barriers.
Ethylene vinyl acetate resin film (EVA film) has been used in optical laminates, both as the sole polymeric film and as a component of a multi-laminate interlayer, but it lacks mechanical strength. Many forms of EVA film have use temperature limitations or poor light stability characteristics, making EVA films fairly undesirable components of glazing products. Cross-linking with peroxide improves temperature stability, but may cause light instability, e.g., in solar cells, in the manner described in U.S. Pat. No. 5,478,402. Impact resistance problems in laminated glass made with EVA film are noted in U.S. Pat. No. 5,759,698.
Glass laminates containing a multi-layer film interlayer made with peroxide cross-linked EVA film are reported in U.S. Pat. No. 4,600,627. These EVA films are used at a thickness of about 0.2-0.4 mm, with a core polymer layer of organic resin film at a thickness of about 50 microns, in a glass laminate of at least 6 mm in total thickness. The U.S. Pat. No. 4,600,627 makes no mention of acoustical properties of the multi-layer laminates, and as described in the patent, the multi-layer resin film glazings would be ineffective security barriers.
Polyvinyl butyral resin interlayer film (PVB film) has been an industry standard for many years in automotive glazing products, particularly in windshield glazing. PVB film offers the benefits of transparency and good adhesion to glass. Glass laminates of PVB film have appropriate glass shattering properties and good mechanical strength. PVB resin also is compatible with additives, such as UV light absorbers and plasticizers. However, the need to moisture-seal PVB laminates contributes significant costs to laminates made with PVB film. When used in a sealed laminate, as in windshield constructions, the tendency of the PVB film to absorb moisture is not a problem. For other vehicular glazings, such as side lights (windows in side doors having no perimeter gasket or seal), conventional PVB film absorbs water too readily to permit acceptable use life. More complex and costly moisture resistant PVB resin formulations, such as those described in U.S. Pat. No. 4,952,457, have been developed for unsealed glazing.
When PVB film is used as the sole interlayer film, glazing laminates do not deliver desirable security performance because they have insufficient rigidity after glass breakage due to the low stiffness of the PVB interlayer. An opening can be made too easily between the glazing and the surrounding body of the vehicle. Neither monolithic glass panes, nor PVB film interlayer laminates, provide an adequate security barrier.
Many different types of polyurethane films have been used in automotive glazings. Some polyurethane films are similar to PVB films in their mechanical properties. In WO 98/50228, certain rigid thermoplastic polyurethanes having a Young""s modulus of about 2,000 MPa are suggested interlayer films for glazings characterized by a high intrusion resistance. Many have slightly better acoustical barrier attributes than PVB films, but fail to provide an adequate security barrier. Furthermore, as described in U.S. Pat. No. 5,368,917 the polyurethane films tested yielded inadequate acoustical insulating barriers for automotive glazing products.
Acoustical barrier requirements for glazing products are defined in U.S. Pat. No. 5,368,917 for the range of frequencies detectable by the human ear, i.e., about 400-15,000 Hertz, with the most critical range falling between 500 to 10,000 Hertz. The standards in this patent are based on the performance of either a 10 mm or a 5 mm thick monolithic glass pane.
Thus, an acoustical barrier glazing has been traditionally understood to be a barrier providing a level of acoustic comfort within the vehicle or building comparable to the level of acoustic comfort provided by a conventional monolithic glass barrier for a given intensity and quality of environmental noise.
Glass (e.g., soda-lime-silicate mineral glass) provides a good acoustical barrier and, over a critical frequency range of about 800 to 10,000 Hz, is most effective at a total glazing thickness of at least about 10 mm. Effective glass glazing may be monolithic, or it may be a double glass pane construction having an air space between the panes. In automotive glazing products, a maximum thickness of about 5 mm is desired. Automotive side lights have been made with double glass panes separated by an air space to achieve superior acoustical barrier properties, but such a construction is generally unacceptable in automotive glazing due to mechanical barrier (safety and security) considerations.
Thin glass sheets have been laminated with specified xe2x80x9cacoustic resinsxe2x80x9d to make an acoustical barrier laminate at a maximum total thickness of 5 mm. An xe2x80x9cacoustic resinxe2x80x9d which is a copolymer of 60-98.5 wt % vinyl chloride, 1-10 wt % glycydyl methacrylate and 0.5-10 wt % ethylene blended with 10-40 wt % plasticizer, and a method for measuring sound transmission in glass laminates containing such modified polyvinyl chloride (PVC) resins, are described in U.S. Pat. Nos. 5,773,102 and 5,368,917. Both vehicular and architectural product applications are described. The acoustic resin is laminated between two transparent, rigid sheets made of glass or polymer. The resultant laminate is characterized by acoustical transmission losses which deviate from a 5 mm tempered glass standard by a maximum of 5 decibels in a frequency range from 800 to 2,000 Hz and a maximum of 3 dB at audible frequencies above 2,000 Hz.
The U.S. Pat. No. 5,773,102 discloses a multi-layer film laminate using the modified PVC resin in combination with conventional safety glass laminate resins, such as polyvinyl butyral and polyurethane, and reports no loss of the modified PVC resin acoustical barrier properties in the multi-layer film laminate. The acoustic resin is used in combination with a third, polymer barrier film, such as a polyethyleneterephthalate (PET) film to prevent migration of plasticizer between the acoustic resin film and the conventional (PVB) film. This combination is described as an inexpensive alternative to the use of a monolithic sheet of the acoustic resin in the glass laminate, and as a means to achieve a safety window with a minimum overall thickness and weight, and a minimum quantity of the expensive acoustic resin.
An xe2x80x9cacoustic PVB filmxe2x80x9d for use as a glazing interlayer is described in JP-A-05138840. The film is a multi-layer construction of films made of two PVB resins comprising, respectively, 70-81.8 mole % degree of butyralization and 60-68 mole % degree of butyralization. A plasticizer is used in both films.
A silicone/acrylate resin vibration damping film is disclosed in U.S. Pat. No. 5,624,763. This silicone/acrylate resin (xe2x80x9cISD resinxe2x80x9d) is suggested for use in applications requiring damping over a wide temperature range (xe2x88x9250 to 200xc2x0 C.) and is described as having damping performance that is substantially independent of temperature in this range. The use of this ISD resin, in combination with two layers of polyester resin and two layers of PVB resin, as an acoustic damping interlayer film for glass laminates is disclosed in DE-1 97 05 586 C1.
None of these xe2x80x9cacoustic resinxe2x80x9d films would be effective an security barrier in glazing laminates, and many exhibit undesirable optical properties.
Furthermore, in newer models of automobiles, a glass thickness of 3 to 5 mm has been specified for side lights so as to minimize the contribution of the glazing to the overall weight of the automobile. At the same time automobile manufacturers seek to reduce the weight of the glazing, they also want to maintain the acoustical barrier and security barrier properties of the glazing. The automobile manufacturers increasingly want to respond to consumer demands for a better quality sound environment in the automobile, and to go beyond existing products generally designed to control only the volume of background noise, without regard to whether the type of noise is offensive to humans. Evidence of this trend can be seen in U.S. Pat. No. 5,805,457, the contents of which are hereby incorporated by reference, wherein roughness, dissonance, sharpness and boom measurements are made over frequencies based upon the musical scale interval to predict aesthetic qualities of noise audible to humans in the interior of a vehicle. In particular, a sharpness value is identified as being significant to human perceptions of noise quality. Lower sharpness values are less offensive to the human ear than high values. Other aesthetic factors include Articulation Index values and loudness values over the relevant frequency range. Articulation Index is described in detail in U.S. Pat. No. 5,729,658, which is hereby incorporated by reference. Articulation Index is a measure of the intelligibility of speech and other sounds in the acoustic range and it may be evaluated in a relative manner over multiple listening conditions. For a passenger in a vehicle, exterior speech or noise that is intelligible is more disturbing than non-intelligible speech or noise. The third aesthetic factor, loudness, and methods for its evaluation and measurement across various transmission barriers are described in many patents, including U.S. Pat. No. 5,464,659, the contents of which are hereby incorporated by reference.
We have now discovered an optically transparent multi-layer film made with selected thickness ratios of a low modulus, flexible, resin film, having at least minor acoustic insulating properties, laminated to one or both surfaces of a high modulus, rigid, resin film, having essentially no acoustic insulating properties. This multilayer film offers the desired automotive glazing interlayer combination of a sufficient acoustical barrier to satisfy aesthetic requirements plus a sufficient mechanical barrier needed to make the new, thinner, light weight security glazing. The multilayer film combination satisfies all of the significant automotive glazing specifications for glass laminate thickness, transparency, safety, security, acoustic performance, weight and cost.
The multi-layer film may be constructed from a relatively inexpensive ethylenic acid copolymer resin, such as ethylene vinyl acetate copolymer resin, co-laminated within specified dimensional ratios with a core film made of materials having security and safety attributes, such as an ionomeric resin or polycarbonate, to provide an effective security barrier. The acoustic performance of this particular interlayer film within a glass laminate is at least equivalent to that of a 3.85 mm thick monolithic glass pane.
To provide a security barrier, the core layer is made from materials having a minimum modulus of 25,000 psi (173 MPa) (by ASTM test method D-638) such that penetration resistance and stiffness are adequate. However, such mechanical properties make these materials poor candidates for acoustical barrier applications because high modulus materials normally exhibit small loss factors (tan xcex4). Furthermore, when these core layer materials are combined with surfaco layer materials having appropriately low modulus values (a maximum of 15,000 psi (104 MPa)) in a multi-layer film, the resultant acoustical barrier appears to function principally by shifting the coincident frequency of the glazing into an aesthetically acceptable spectral range, rather than by merely insulating against the sound transmission. The resultant acoustical barrier properties are unexpected, given the material properties and thickness of the materials employed in the glazing.
When used in glass laminates, this multi-layer film has optical clarity, along with good adhesion to glass, the mechanical properties needed to meet safety and security standards and moisture resistance required for automotive glazing products, including automotive side lights. Optically transparent glazing containing the acoustical barrier, security barrier multi-layer film made according to our invention also may be used in less demanding glazing applications, such as architectural glazing.
The invention is an optically transparent glazing, measuring about 3 mm to 5 mm in total thickness, and having an interlayer film, the interlayer film comprising at least two polymeric film layers: a core film layer having a modulus of at least 25,000 psi (173 MPa), and a surface film layer having a maximum modulus of 15,000 (104 MPa) at 50 to 10,000 Hz and 20xc2x0 C.; and the glazing having an acoustical barrier insulating capacity at least equivalent to that of a 3.85 mm thick monolithic pane of glass, an Articulation Index value of less than 64.2% at 50 to 10,000 Hz, a sharpness value of less than 150 at 50 to 10,000 Hz, a penetration resistance of at least 9 meters in test method ECE R43 A6 4.2, and a maximum haze of 4%. The interlayer film has a bending stiffness of at least 0.01 Pa*m3. The interlayer film comprises a surface film layer having a maximum tan delta value of 0.6 at 50 to 10,000 Hz and 20xc2x0 C. The interlayer film preferably comprises one core film layer of between 1.0 and 1.7 mm in thickness within two surface film layers, each between 0.2 and 0.6 mm in thickness. The glazing preferably comprises a glass/interlayer film glass sandwich having a glass/film thickness ratio from 4.2/0.8 to 1.0/2.8.